A coated paper has a problem that when the gloss of coated surface is excessively good, it causes glare under strong light to lead to eye strain. Therefore, the interest in high quality matte paper, which has low glare and gives subdued and relaxed feeling, has been recently increased. In particular, the market demands of the high quality matte paper show a tendency to increase in North America and Europe.
Generally, the coated paper is prepared by coating inorganic pigments such as clay, ground calcium carbonate (GCC), aluminum hydroxide, titanium oxide etc., on paper, wherein the gloss and nature of the coated paper surface are significantly influenced by inorganic pigment property. As an example, in the case where the clay is used, print gloss and adhesion are good, but brightness property is degraded. On the other hand, in the case where the inorganic pigment such as the ground calcium carbonate is used, it has advantages that glossiness is relatively low, ink receptivity is good and brightness is excellent as well as since it is inexpensive, cost reduction is achieved, as compared to the case where the clay is used.
The inorganic pigments such as the ground calcium carbonate, etc., for the purpose of matte coating have generally been used up to now. In this case, however, the ink is too rapidly infiltrated into a coating layer so that the print gloss is low and the adhesion is degraded. Therefore, there has been reported an example where different physical properties are compromised by properly mixing the clay and the ground calcium carbonate so that they are optimized (TAPPI Journal (1998), vol. 81, no. 11, p. 175).
Recently, the matte coated paper has been produced using talc. However, the talc has problems that it has poor dispersibility and its viscosity is excessively increased with the passage of time. An example of improving the problems as above has been reported (TAPPI Journal (2004), vol. 3, no. 8, p. 25).
Furthermore, Japan Laid-Open No. H7-166492 and International Application WO 97-032082, and the like are technologies that use organic pigments in a hollow structure, and include the contents that prepare the coating layer containing calcium carbonate, which is inorganic pigment, and the organic pigment in the hollow structure with shock-absorbing nature. Preferably, there has been reported that the coated paper is not subject to calandering in order to better implement the matted property.
Meanwhile, the structure and surface nature of the entire coating layer are varied according to the physical and chemical properties of paper coating latex. This has a significant effect on printability such as, white paper gloss, print gloss, ink drying rate, etc. When the particle diameter of latex becomes large, the content of latex in the coating layer composition becomes low, or the glass transition temperature becomes high, the inorganic pigment arrangement is easily made so that the white paper gloss is increased but the adhesion is degraded. On the other hand, when the particle diameter of latex becomes small, the content of latex in the coating layer composition becomes large, or the glass transition temperature becomes low, the air permeability of the coating layer is degraded so that there is ink solvent on the surface of the coating layer until ink components have a stabilized arrangement after printing, making it possible to improve the print gloss. However, this is the method that is contrary to the method of improving the white paper gloss, wherein this method has advantages that the ink drying rate is degraded and causes problems such as print mottle and set off phenomenon, etc.
Also, the surface energy of paper coating latex has an effect on the printability such as the white paper gloss, the print gloss, the ink drying rate, etc. For example, when the surface of latex has large hydrophilic property or functional group with large chemical resistance against ink solvent, the infiltration rate of in components, which are hydrophobic property, is slow so that the print gloss is improved.
As described above, the white paper gloss can be lowered and the print gloss can be improved by means of the method of changing the latex properties, such as the method of controlling the size of the particle diameter of paper coating latex, the glass transition temperature, and the surface energy; however, the method remarkably degrades the ink dryness and cannot help using the method of controlling the inorganic/organic pigments in order to reveal the matte coated paper properties and at the same time, has a difficulty in improving the printability such as adhesion, water resistance, inking property, ink dryness, etc.